Directional coupler

ABSTRACT

A directional coupler includes first and second dielectric layers, and an intermediate dielectric layer disposed therebetween. The first dielectric layer has one surface formed with a first coupling line, and the second dielectric layer has one surface formed with a second coupling line. Outside the first dielectric layer, there is a third dielectric layer with a grounding electrode on a surface thereof. Outside the second dielectric layer, there is a fourth dielectric layer with a grounding electrode on a surface thereof. The dielectric layers are laminated together so that a dielectric layer is interposed between the grounding electrode and an adjacent one of the coupling lines. The first and second coupling lines are aligned with each other in the direction of laminate. Each of the first and second coupling lines has a spiral configuration including first to fifth sequential portions. The first portion is substantially parallel with an edge of the dielectric layer on which the line is formed. Each of the second to fifth portions is connected with and perpendicular to the preceding portion, with the fifth portion being inside the first portion.

TECHNICAL FIELD

The present invention relates to a directional coupler forelectromagnetically coupling a signal input primary line with anauxiliary line. More specifically, the present invention pertains to adirectional coupler having conductors provided on a layer of adielectric material to thereby provide paired lines to be coupled.

BACKGROUND ART

The U.S. Pat. No. 5,329,263 issued on Jul. 12, 1994 to Kazuaki Minamidiscloses a directional coupler having a dielectric substrate providedon one side surface with a conductive grounding electrode which extendsthroughout the surface and on the other side surface with paired signaltransmitting coupling lines of a conductive material. These lines areformed on the surface of the substrate by parallelly extending portions,each of the parallelly extending portions of the coupling lines havingopposite ends provided with leads which extends perpendicularly to theparallelly extending portions.

One of the coupling lines is connected through the lead at one endthereof with an input port and through the lead at the other end with anoutput port. The other coupling line is connected through the lead atone end with a second output port and through the lead at the other endwith an isolation port. The coupling lines and the leads are connectedtogether through a deposition of a conductive metal such as gold.

In this type of coupler, the isolation port is connected normally to theground. As a signal is applied to the input port of the one couplingline, a corresponding signal is produced at the output of the onecoupling line. A signal is also produced through electromagneticcoupling between the paired coupling lines at the second output port ofthe other coupling line. When an input signal is applied to the outputport of the one coupling line an output is produced at the input port ofthe one coupling line, and at the same time an output is produced at thesecond output port of the other coupling line with a level which isdifferent from the level when the input signal is applied to the inputport. The difference in the signal level at the second output port ofthe other coupling line between the occasion when the input signal isapplied to the input port of the one coupling line and the occasion whenthe input signal is applied to the output port is defined as thedirectionality or isolation of the coupler.

It has been recognized that the coupler shows a large directionality inresponse to an input signal wherein the length of the parallellyextending coupling lines is equal to 1/4 of the wavelength. It is notedfurther that the coupling power of the coupler is dependent on thedistance between the coupling lines whereby a tight coupling is producedwith a small distance whereas a weak coupling is produced with a largedistance. In the coupler of the type disclosed by the aforementionedU.S. patent, the coupling lines are formed on a surface of thedielectric substrate. It should however be noted that the coupling linesmay be embedded in the body of the dielectric body. In that case, theeffective line wavelength is decreased to λ/4 ε_(r), where ε_(r)designates a specific dielectric constant and λ the wavelength of theinput signal. Thus, the coupler size can be decreased by using amaterial of higher specific dielectric constant. It should therefore beunderstood that a dielectric material of an appropriate specificdielectric constant may be used for decreasing the size of a directionalcoupler.

In the case where a dielectric body is of a laminated structure whereina plurality of dielectric layers are laid one over the other, thecoupling lines can be provided between adjacent dielectric layers. Inthis structure, the paired coupling lines may be arranged on theopposite sides of a dielectric layer.

In a directional coupler having coupling lines embedded in a dielectricbody as described, the dielectric layers are generally formed of amaterial of a high dielectric constant. However, using a dielectricmaterial of high dielectric constant is likely to cause a decrease inimpedance of the signal line conductor, so that it is required toincrease the distance between the signal line conductor and the groundelectrode or to decrease the width of the signal line conductor.Dielectric layers are formed by sintered ceramics. It should thereforebe noted that to increase the distance between the signal lineconductors and the ground electrode will cause a corresponding increasein the thickness of the dielectric layer. Thus, an increased time willbe required for sintering process to remove binder and an increasedprocessing time will therefore be required for manufacture.Particularly, in a structure wherein paired signal lines are provided atthe opposite sides of a dielectric layer, the thickness of thedielectric substrate is undesirably increased so that the structure isdisadvantageous in making the device compact. It should further be notedthat the structure having a decreased signal line conductor widthinvolves another problem of transmission loss in the signal lineconductor being increased.

DISCLOSURE OF THE INVENTION

The present invention is therefore aimed to solve the aforementionedproblems in conventional directional coupler and has an object toprovide a directional coupler which is compact and thin in structure andeasy to manufacture.

Another object of the present invention is to provide a directionalcoupler of a high isolation characteristics.

According to the present invention, in order to accomplish the aboveobjects, a first dielectric layer is provided at least on one surfacewith a first coupling line and a second dielectric layer is provided atleast on one surface with a second coupling line, the dielectric layersbeing laid one over the other so that the first and second couplinglines are aligned with each other with dielectric material interposedtherebetween, two outer dielectric layers each having a groundingelectrode extending to cover substantially throughout the surfacethereof, the outer dielectric layers being laid over outer surfaces ofthe first and the second dielectric layers respectively with dielectricmaterial interposed between the coupling lines and the groundingelectrodes, each of the first and second coupling lines being of aconvolute configuration of at least 1/3 turn. The term convoluteconfiguration as herein used means a configuration corresponding to atleast a portion of at least one turn of a spiral configuration.

According to one aspect of the present invention, the directionalcoupler comprises a first dielectric layer having a first coupling lineformed on one surface thereof, a second dielectric layer having a secondcoupling line formed on one surface thereof, an intermediate dielectriclayer disposed between the first and second dielectric layers, a thirddielectric layer disposed outside the first dielectric layer and havinga grounding electrode extending substantially throughout a surfacethereof, a fourth dielectric layer disposed outside the seconddielectric layer and having a grounding electrode extendingsubstantially throughout a surface thereof, the layers being laid oneover the other with a dielectric layer interposed between each groundingelectrode and adjacent one of the coupling lines, the first and secondcoupling lines being arranged so that they are aligned with each otherin a direction of laminate, each of the first and second coupling linesbeing of a spiral configuration including a first portion which extendsin parallel with one edge of the dielectric layer on which the couplingline is formed, a second portion having one end connected with one endof the first portion and extending substantially perpendicularly to thefirst portion, a third portion having one end connected with the otherend of the second portion and extending substantially perpendicularly tothe second portion, a fourth portion having one end connected with theother end of the third portion and extending substantiallyperpendicularly to the third portion, and a fifth portion having one endconnected with the other end of the fourth portion and located insidethe first portion to extend substantially perpendicularly to the fourthportion.

Outside the grounding electrode, there is formed at least one dielectriclayer to provide a protective layer. For the purpose, either one or bothof the third and fourth dielectric layers may be disposed so that thegrounding electrodes formed thereon are located inside the respectivelayers, or alternatively, a further dielectric layer may be laid overthe third or fourth dielectric layer. In the structure of this aspect,each of the first, and second coupling lines are connected at the otherend of the first portion and the other end of the fifth portion withleads which are extending to an edge portion of the laminated structureto form external connecting ports. For the purpose, the other end of thefirst portion may be connected through a lead to a port on the edgeportion of the laminated structure. The other end of the fifth portionmay be connected through the dielectric layer adjacent to the couplingline with a lead formed on a surface of another dielectric layer whichis in turn connected with the port on the edge portion of the laminatedstructure.

In the directional coupler of the present invention, each of the firstand second coupling lines may be formed in two or more dielectriclayers. It should further be noted that in accordance with the presentinvention each of the coupling lines preferably has an outermost edgewhich is located in a projection in the direction of laminate thicknessinside by a predetermined distance from the edge of the groundingelectrode. It is possible to accomplish an extremely excellent isolationcharacteristics by choosing the predetermined distance at least 0.3 mm,preferably 0.45 mm.

In accordance with a further aspect of the present invention, thedielectric layers at the opposite sides of each of the first and secondcoupling lines are formed of a material having a high specificdielectric constant, and other dielectric layers from a material havinga relatively low specific dielectric constant. This structure providesadvantages in that the signal wavelength can be decreased due to thedielectric layers of a high specific dielectric constant at the oppositesides of each coupling line, and it is not necessary to increase thesubstrate thickness because the line impedance will not be substantiallyincreased by forming the other dielectric layers from a material ofrelatively low specific dielectric constant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a directional coupler of alaminated structure in accordance with the present invention;

FIG. 2 is a perspective view showing an external appearance of thedirectional coupler shown in FIG. 1;

FIG. 3 is a sectional view taken along the line III--III in FIG. 2;

FIG. 4 is a sectional view similar to FIG. 3 but showing anotherembodiment of the present invention;

FIG. 5 is an exploded perspective view of a directional coupler similarto FIG. 1 but showing a further embodiment of the present invention;and,

FIG. 6 is a diagram showing influences of the distance between edges ofthe coupling line and the grounding electrode on the isolationcharacteristics in the directional coupler in accordance with thepresent invention, wherein 6(a) is a sectional view of the coupler forshowing the manner of measuring the distance, 6(b) a plan view showingprojections in the direction of laminate thickness of the coupling lineand the grounding electrode, 6(c) a diagram showing the isolationcharacteristics under the distance of 0.2 mm, and 6(d) a diagram showingthe isolation characteristics under the distance of 0.45 mm.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described with reference toembodiments. Referring first to FIG. 1, there is shown a directionalcoupler 1 in accordance with one embodiment which is formed by sinteringa plurality of laminated green sheets of dielectric material. Thecoupler 1 includes a first dielectric layer 3 having a first couplingline 2 formed thereon, a second dielectric layer 5 having a secondcoupling line 4 formed thereon, and an intermediate dielectric layer 6disposed between the dielectric layers 3 and 5.

The first coupling line 2 is formed on the top surface of the firstdielectric layer 3. The coupling line 2 is of a spiral configurationincluding a first portion 2a extending substantially in parallel with anedge 3a of the first dielectric layer 3, a second portion 2b having oneend connected with one end of the first portion 2a and extendingsubstantially perpendicularly to the first portion 2a, a third portion2c having one end connected with the other end of the second portion 2band extending substantially perpendicularly to the second portion, afourth portion 2d having one end connected with the other end of thethird portion and extending substantially perpendicularly to the thirdportion 2c, and a fifth portion 2e having one end connected with theother end of the fourth portion 2d and located inside the first portion2a to extend substantially perpendicularly to the fourth portion 2d.

The second coupling line 4 is formed on the top surface of the seconddielectric layer 5. The second coupling line 4 includes a first portion4a, a second portion 4b, a third portion 4c, a fourth portion 4d and afifth portion 4e which are aligned in the direction of laminatethickness to the first portion 2a, the second portion 2b, the thirdportion 2c, the fourth portion 2d and the fifth portion 2e,respectively. In accordance with the present invention, a satisfactoryresult can be obtained with the coupling lines 2 and 4 each having thefirst to third portions. In this instance, the coupling line comprisedof the first to third portions constitute a part of a spiralconfiguration. The term "convolute configuration" is herein used toinclude this configuration as well as a spiral configuration.

A second intermediate dielectric layer 7 is laid over the firstdielectric layer 3. The first portion 2a of the first coupling line 2formed on the first dielectric layer 3 has an end connected with a lead8 which is in turn connected with a first port 8a provided on an edge 3aof the first dielectric layer 3. The second intermediate dielectric,layer 7 is provided on the top surface with a lead 9. The lead 9 hasone end connected through the dielectric layer 7 with an end of thefifth portion 2e of the first coupling line 3. The lead 9 extends to anedge portion of the dielectric layer 7 to be connected with a secondport 9a formed thereon.

A third intermediate dielectric layer 10 is provided beneath the seconddielectric layer 5. The first portion 4a of the second coupling line 4formed on the second dielectric layer 5 has an end connected with a lead11 which is in turn connected with a third port 12 formed on an edge 5aof the second dielectric layer 5, the edge 5a being at a side oppositeto the side where the edge 3a is located on the first dielectric layer3. The third intermediate dielectric layer 10 is formed on the topsurface with a lead 13. The lead 13 has one end which is connectedthrough the dielectric layer 5 with an end of the fifth portion 4e ofthe second coupling line 4. The other end of the lead 13 is connectedwith a fourth port 13a which is provided on an edge 10a of thedielectric layer 10, the edge 10a being vertically aligned with the edge5a of the second dielectric layer 5.

Above the second intermediate dielectric layer 7, there is laminated athird dielectric layer 14 for a grounding electrode. Similarly, a fourthdielectric layer 15 is laminated beneath the third intermediatedielectric layer 10 for another grounding electrode. A groundingelectrode 16 is formed on the top surface of the third dielectric layer14 to cover substantial part of the surface. Similarly, a groundingelectrode 17 is formed on the top surface of the fourth dielectric layer14. The grounding electrodes 16 and 17 are connected with groundingports 18 and 19 provided at the opposite side edges of the dielectriclayers. A dielectric layer 20 is laminated on the top surface of thethird dielectric layer 14 to provide a protective layer.

The directional coupler 1 of the aforementioned laminated structure isshown in FIG. 2. The coupler 1 has port electrodes for providing ports8a, 9a, 12, 13a, 18 and 19 at edge portions thereof. FIG. 3 shows asection of the coupler 1. In this embodiment, the dielectric layers inthe laminate are of the same specific dielectric constant.

FIG. 4 is a sectional view similar to FIG. 3 but shows anotherembodiment. In this embodiment, corresponding parts are designated bythe same reference characters as in the previous embodiment, anddetailed description will be omitted. In this embodiment, anotherdielectric layer 21 is disposed between the first dielectric layer 3 andthe intermediate dielectric layer 6. The first dielectric layer 3 andthe second intermediate dielectric layer 7 which is located above thefirst dielectric layer 3 with the first coupling line 2 interposedtherebetween, and the second dielectric layer 5 and the intermediatedielectric layer 6 which is located above the second dielectric layer 5with the second coupling line 4 interposed therebetween are formed of amaterial having a high specific dielectric constant. The otherdielectric layers are made of a material having a low specificdielectric constant. In this embodiment, it is possible to decrease thesignal wavelength by providing the dielectric layers having a couplingline interposed therebetween with a high specific dielectric constant.Since the other dielectric layers are of a material having a lowspecific dielectric constant, the line impedance is not significantlydecreased.

FIG. 5 shows a further embodiment of the present invention. In thisembodiment, the laminated structure is substantially the same as in theembodiment of FIG. 1, however, the second intermediate dielectric layer7 is formed with a spiral pattern 7a which provides a portion of thefirst coupling line and the spiral pattern 7a has an outer end connectedwith the lead 9. The inner end of the spiral pattern 7a is connectedthrough the dielectric layer 7 with an end of the fifth portion 2e ofthe coupling line 2 on the first dielectric layer 3. It will thereforebe understood that the first coupling line 2 is of a two layerstructure. Similarly, the third intermediate dielectric layer 10 isformed with a conductor providing a spiral pattern 10a having an outerend connected with the lead 13. The inner end of the spiral pattern 10ais connected through the dielectric layer 5 with an end of the fifthportion 4e of the coupling line 4 on the second dielectric layer 5. Thisstructure provides a second coupling line of two layer construction. Inother respects, the structures are the same as in the embodiment of FIG.1.

Referring now to FIG. 6, there is shown in (a) and (b) the relationshipbetween the coupling line E and the grounding electrode G in the form ofprojections in the direction of the laminate thickness. As showntherein, the coupling line E has an outer edge which is located insidethe edge of the grounding electrode by a distance d. In FIG. 6(c), thereis shown an isolation characteristics obtained with the distance d of0.2 mm. FIG. 6(d) shows an isolation characteristics obtained with thedistance of 0.45 mm. In these drawings, it will be understood that abetter isolation characteristics can be obtained with a larger distanced. In accordance with the present invention, a significant isolationcharacteristics can be obtained with the distance d of 0.3 mm or larger.

I claim:
 1. A directional coupler including:a first spiral patternstructure comprising a first dielectric layer provided at least on onesurface with a single first coupling line and a second dielectric layerprovided at least on one surface with a single second coupling line, thedielectric layers being laid one over the other so that the first andsecond coupling lines are located with dielectric material interposedtherebetween, one end of the first coupling line being connected withone end of the second coupling line through a conductor passing throughthe dielectric material interposed between the first and second couplinglines to form a first spiral coupling line pattern; a second spiralpattern structure comprising a third dielectric layer provided at leaston one surface with a single third coupling line and a fourth dielectriclayer provided at least on one surface with a single fourth couplingline, the third and fourth dielectric layers being laid one over theother so that the third and fourth coupling lines are located withdielectric material interposed therebetween, one end of the thirdcoupling line being connected with one end of the fourth coupling linethrough a conductor passing through the dielectric material interposedbetween the third and fourth coupling lines to form a second spiralcoupling line pattern; said first and second spiral pattern structurebeing laid one over the other so that the first and second spiralcoupling line patterns are located with dielectric material interposedtherebetween; two outer dielectric layers each having a groundingelectrode extending to cover substantially throughout the surfacethereof, the outer dielectric layers being laid over outer surfaces ofthe first and the second spiral pattern structures, respectively, withdielectric material interposed between the spiral coupling line patternsand the grounding electrodes, each of the first and second spiralcoupling line patterns including a coupling line of a convoluteconfiguration of at least one turn; wherein the dielectric layerslocated at opposite sides of each of the first and second coupling linesare made of a material having a high specific dielectric constant, andother dielectric layers are made of a material having a relatively lowdielectric constant.
 2. A directional coupler in accordance with claim1, which includes at least one dielectric layer outside each of thegrounding electrodes for providing a protective layer.
 3. A directionalcoupler in accordance with claim 2, wherein at least one of saiddielectric layers having the grounding electrodes formed thereon islocated with the grounding electrode inside the associated layer.
 4. Adirectional coupler in accordance with claim 1, wherein each of thefirst and second coupling lines is formed on at least two dielectriclayers.
 5. A directional coupler including a first dielectric layerhaving a single first coupling line formed on one surface thereof, asecond dielectric layer having a single second coupling line formed onone surface thereof, an intermediate dielectric layer disposed betweenthe first and second dielectric layers, a third dielectric layerdisposed outside the first dielectric layer and having a groundingelectrode extending substantially throughout a surface thereof, a fourthdielectric layer disposed outside the second dielectric layer and havinga grounding electrode extending substantially throughout a surfacethereof, the layers being laid one over the other with a dielectriclayer interposed between each grounding electrode and an adjacent one ofthe coupling lines, the first and second coupling lines being arrangedso that they are located one over the other in a direction oflamination, each of the first and second coupling lines being of aspiral configuration including a first portion which extends in parallelwith one edge of the dielectric layer on which the coupling line isformed, a second portion having one end connected with one end of thefirst portion and extending substantially perpendicularly to the firstportion, a third portion having one end connected with the other end ofthe second portion and extending substantially perpendicularly to thesecond portion, a fourth portion having one end connected with the otherend of the third portion and extending substantially perpendicularly tothe third portion, and a fifth portion having one end connected with theother end of the fourth portion and located inside the first portion toextend substantially perpendicularly to the fourth portion, each of thefirst and second coupling lines having an edge which is located in aprojection in the direction of lamination inside by a predetermineddistance from an edge of the grounding electrode;wherein each of thefirst and second coupling lines are connected at the other end of thefirst portion and the other end of the fifth portion with leads whichextend to an edge portion of the laminated structure to form externalconnecting ports.
 6. A directional coupler in accordance with claim 5,which includes at least one dielectric layer outside each of thegrounding electrodes for providing a protective layer.
 7. A directionalcoupler in accordance with claim 6, wherein at least one of saiddielectric layers having the grounding electrodes formed thereon islocated with the grounding electrode inside the associated layer.
 8. Adirectional coupler in accordance with claim 5, wherein the other end ofthe first portion is connected through a lead to a port on the edgeportion of the laminated structure and the other end of the fifthportion is connected through the dielectric layer adjacent to thecoupling line with a lead formed on a surface of another dielectriclayer which is in turn connected with the port on the edge portion ofthe laminated structure.
 9. A directional coupler in accordance withclaim 5, wherein each of the first and second coupling lines is formedon at least two dielectric layers.
 10. A directional coupler including afirst dielectric layer having a single first coupling line formed on onesurface thereof, a second dielectric layer having a single secondcoupling line formed on one surface thereof, an intermediate dielectriclayer disposed between the first and second dielectric layers, a thirddielectric layer disposed outside the first dielectric layer and havinga grounding electrode extending substantially throughout a surfacethereof, a fourth dielectric layer disposed outside the seconddielectric layer and having a grounding electrode extendingsubstantially throughout a surface thereof, the layers being laid oneover the other with a dielectric layer interposed between each groundingelectrode and an adjacent one of the coupling lines, the first andsecond coupling lines being arranged so that they are located one overthe other in a direction of lamination, each of the first and secondcoupling lines being of a spiral configuration including a first portionwhich extends in parallel with one edge of the dielectric layer on whichthe coupling line is formed, a second portion having one end connectedwith one end of the first portion and extending substantiallyperpendicularly to the first portion, a third portion having one endconnected with the other end of the second portion and extendingsubstantially perpendicularly to the second portion, a fourth portionhaving one end connected with the other end of the third portion andextending substantially perpendicularly to the third portion, and afifth portion having one end connected with the other end of the fourthportion and located inside the first portion to extend substantiallyperpendicularly to the fourth portion, each of the first and secondcoupling lines having an edge which is located in a projection in thedirection of lamination inside by a predetermined distance from an edgeof the grounding electrode;wherein the dielectric layers located atopposite sides of each of the first and second coupling lines are madeof a material having a high specific dielectric constant, and otherdielectric layers are made of a material having a relatively lowdielectric constant.
 11. A directional coupler in accordance with claim10, which includes at least one dielectric layer outside each of thegrounding electrodes for providing a protective layer.
 12. A directionalcoupler in accordance with claim 11, wherein at least one of saiddielectric layers having the grounding electrodes formed thereon islocated with the grounding electrode inside the associated layer.
 13. Adirectional coupler in accordance with claim 10, wherein each of thefirst and second coupling lines are connected at the other end of thefirst portion and the other end of the fifth portion with leads whichare extending to an edge portion of the laminated structure to formexternal connecting ports.
 14. A directional coupler in accordance withclaim 13, wherein the other end of the first portion is connectedthrough a lead to a port on the edge portion of the laminated structureand the other end of the fifth portion is connected through thedielectric layer adjacent to the coupling line with a lead formed on asurface of another dielectric layer which is in turn connected with theport on the edge portion of the laminated structure.
 15. A directionalcoupler in accordance with claim 10, wherein each of the first andsecond coupling lines is formed on at least two dielectric layers.